Transcript Unit 3 Lesson 3 Assignment Operator

Unit 3, Lesson 3
Math Operations, Assignment
Operators, and Arithmetic
Operators
Mr. Dave Clausen
La Cañada High School
http://www.lcusd.net/dclausen
Assignment Operator
• You have used the assignment operator (=)
to initialize variables, so you already know
most of what there is to know about the
assignment operator
• The assignment operator changes the
value of the variable to the left of the
operator.
• For example:
i = 25;
//changes the value of i to 25
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Code List 3-1
#include <iostream.h>
//iassign.cpp
iassign.txt
//declaring and initializing variables in two steps
int main ()
{
int i;
// declare i as an integer
i=1000;
// assign the value 1000 to i
cout << i << endl;
i=25;
// assign the value 25 to i
cout << i << endl;
return 0;
}
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Code List 3-2
#include <iostream.h>
//multint.cpp
multint.txt
//declaring multiple variables in one step
//initializing multiple variables in one step
int main ()
{
int i, j, k;
// declare i, j, and k as integers
i =j=k=10; //initialize all of the variables to 10
cout << i << ‘\n’;
cout << j << ‘\n’;
cout << k << ‘\n’;
return 0;
}
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Declare & Initialize
• Constants MUST be declared and
initialized in the same statement.
• Variables MAY be declared and initialized
in the same statement.
• For example:
int number = 10;
double result = 0.0;
char letter = ‘ ‘; // a space
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Arithmetic Operators
• A specific set of arithmetic operators is used to
perform calculations in C++
• These arithmetic operators, shown in Table 3-1,
may be somewhat familiar to you
• Addition and subtraction and performed with the
familiar + and - operators
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Table 3-1
The arithmetic operators are used with two
operands, as in the examples in Table 3-1
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Using Arithmetic Operators
Arithmetic operators are most often used on the right
of an assignment operator as shown in the
examples in Table 3-2
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Assignment Operator vs.
The Equal Sign
• The assignment operator (=) functions differently
in C++ from the way the equal sign functions in
Algebra.
• Look at the following statement:
x = x + 10;
• This statement is False in Algebra.
• In C++, the old value of x is incremented
by 10 and then assigned to the new value of
x.
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Code List 3-3
// assign.cpp
assign.txt
#include <iostream.h>
int main ()
{
int i = 2;
//declare and initialize in one step
int j = 3;
//declare and initialize in one step
int k = 4;
//declare and initialize in one step
int l;
float a = 0.5;
//declare and initialize in one step
float b = 3.0;
//declare and initialize in one step
float c;
1 = i + 2;
cout << 1 << ‘\n’;
1 = 1- j;
cout << 1 << ‘\n’;
1 = i * j * k;
cout << 1 << ‘\n’;
1 = k / i;
cout << 1<< ‘\n’;
c = b * a;
cout << c << '\n';
c = b / a;
cout << c << '\n';
getch();
return 0;
Mr. Dave Clausen
}
10
Arithmetic operators are used to create
expressions
Expression
cost = price + tax
Result of expression
cost is assigned the value of price plus tax
owed = total – discount owed is assigned the value of total minus discount
area = l * w
one_eighth = 1 / 8
r=5%2
x = -y
area is assigned the value of l times w
one_eighth is assigned the value of 1 divided by 8
r is assigned the integer remainder of 5 divided by 2
by using the modulus operator
x is assigned the value of -y
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Assignment Statements
• A Method of putting values into memory
locations
 variable name = value;
 a variable name = expression;
• Assignment is made from right to left
• Constants can’t be on left side of statement
• Expression is a constant or variable or
combination thereof
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Assignment Statements
• Values on right side not normally changed
• Variable and expression must be of
compatible data types (more later)
• Previous value of variable discarded to
make room for the new value
• For now char, int, and double are
compatible with each other
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Assignment Examples
•
•
•
•
score1 = 72.3;
score2 = 89.4;
score3 = 95.6;
average = (score1 + score2 + score3) / 3.0
 why not divide by 3 instead of 3.0?
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The Modulus operator
• The Modulus
Operator, which can
be used only for
integer division,
returns the remainder
rather than the
quotient.
• As shown in figure
3-1, integer division
is similar to the way
you divide manually
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Code List 3-4
// remain.cpp
remain.txt
// Calculations using assignment statements
#include <iostream.h>
int main ()
{
int dividend, divisor, quotient, remainder;
/ / ------------------------Input---------------------------cout << “Enter the dividend “;
cin >> dividend;
cout << “Enter the divisor “;
cin >> divisor;
/ / ----------------------Calculations-----------------------quotient = dividend / divisor;
remainder = dividend % divisor;
/ / -------------------------Output-----------------------------cout << “the quotient is “ << quotient;
cout << “ with a remainder of “ << remainder << ‘\n’;
return 0;
}
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Code List 3-5
// remain2.cpp
remain2.txt
//calculations in cout statements - while it can be done, please DON’T DO THIS
#include <iostream.h>
int main()
{
int dividend, divisor;
// ---------------------Input------------------------------cout << “enter the dividend”;
cin >> dividend;
cout << “Enter the divisor”;
cin >> divisor;
// ---------------Calculations in the Output------------Don’t Do This For My Class
cout << “the quotient is “ << dividend/divisor;
cout << “with a remainder of “ << dividend % divisor << ‘\n’;
return 0;
}
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Incrementing and Decrementing
• Adding or subtracting 1 from a variable is
very common in programs. Adding 1 to a
variable is called incrementing, and
subtracting 1 from a variable is called
decrementing.
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The ++ and -- Operators
• C++ provides operators for incrementing and
decrementing. In C++, you can increment an
integer variable using the ++ operator, and
decrement using the -- operator, as shown in Table
3-3
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Code List 3-6
// inc_dec.cpp
inc_dec.txt
#include <iostream.h>
int main()
{
int j;
// declare j as int
j=1;
// initialize j to 1
cout << “j=“ << j << ‘\n’;
j++;
//increment j
cout << “j=“ << j << ‘\n’;
j--;
//decrement j
cout << “j=“ << j << ‘\n’;
return 0;
}
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Variations of Increment and
Decrement
At first glance, the ++ and – operators seem
very simple. But there are two ways that
each of these operators can be used. The
operators can be placed either before or
after the variable. The location of the
operators affects the way they work.
c++ or ++c
c- - or - - c
We will use c++ and c- - for this class
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Order of Operations
• You may recall from your math classes the rules related to the order in
which operations are performed. These rules are called the order of
operations. The C++ compiler uses a similar set of rules for its
calculations. Calculations are processed in the following order
• Minus sign used to change sign (-)
• Multiplication and division (*/%)
• Addition and subtraction (+ -)
•C++ lets you use parentheses to
change the order of operations.
For example, consider the two
statements in Figure 3-2.
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Code List 3-7
/ / order.cpp
#inlcude <iostream.h>
order.txt
int main ()
{
int answer
answer = 1 + 2 * 2 + 3;
cout << answer << ‘\n’;
answer = (1 + 2) * (2 + 3);
cout << answer << ‘\n’;
answer = 1 + 2 * (2 + 3);
cout << answer << ‘\n’;
answer = (1 +2) * 2 + 3 ;
cout << answer << ‘\n’;
return 0;
}
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Integer Arithmetic
•
•
•
•
•
+
*
/
%
Addition
Subtraction
Multiplication
Quotient (Integer Division)
Remainder (Modulus)
Quotient
Remainder
Divisor Dividend 
Divisor
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Integer Order Of Operations
• Expressions within parentheses
 nested parentheses: from inside out
• * (multiplication), % (modulus), / (division)
 from left to right
• + (addition), - (subtraction)
 from left to right
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Integer Arithmetic (Examples)
(3-4)*5 =
3 * (-2) =
17 / 3 =
17 % 3 =
17 / (-3) =
-17 % 7 =
-42+50%17=
-5
-6
5
2
-5
-3
-26
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Real Number Arithmetic
• Type double:
•
•
•
•
+
*
/
Addition
Subtraction
Multiplication
Division
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Real Number
Order Of Operations
• Expressions within parentheses
 nested parentheses: from inside out
• * (multiplication), / (division)
 from left to right
• + (addition), - (subtraction)
 from left to right
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Real Number Arithmetic
(Examples)
2.0 * (1.2 - 4.3) =
2.0 * 1.2 - 4.3 =
-12.6 / (3.0 + 3.0) =
3.1 * 2.0 =
-12.6 / 3.0 + 3.0 =
-6.2
-1.9
-2.1
6.2
-1.2
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Compound Assignments
• “Short hand” notation for frequently used
assignments (We will not use these for
readability of our programs.)
Short hand
Longer form
x += y
x=x+y
x -= y
x=x-y
x *= y
x=x*y
x /= y
x=x/y
x %= y
x=x%y
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Sample Program
Here is a program that prints data about the
cost of three textbooks and calculates the
average price of the books:
Books.cpp
Books.txt
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Input
• Cin (pronounced see-in)
 gets data from keyboard, the standard input stream
 extractor operator >>
• obtain input from standard input stream and direct it to a
variable (extract from stream to variable)
 inserter operator <<
• insert data into standard output stream
 EGG ILL
• Extractor Greater Greater, Inserter Less Less
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Input
• Data read in from keyboard must match the
type of variable used to store data
• Interactive Input
 enter values from keyboard while the program
is running
 cin causes the program to stop and wait for the
user to enter data from the keyboard
 prompt the user for the data (user friendly)
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Input: Sample Programs
No prompt for any of the data values:
input.cpp
input.txt
One prompt for each data value (preferred)
triples.cpp
triples.txt
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